This invention relates to a semiconductor device and a method of testing the same and, in particular, to a method of checking a forming state of a metal film in an opening formed in an interlayer insulating film.
Recently, a diameter of an opening, such as a contact hole, a through hole and a via hole, has been reduced with a high integration of a semiconductor device. The opening is generally formed in an interlayer insulating film. In this case, an aspect ratio which is obtained by dividing a depth of the opening by the diameter has been increased because the depth of the opening is almost kept constant. Therefore, the opening is not sufficiently covered with a metal film, such as aluminum film, through the conventional sputtering method. Consequently, a connecting resistance becomes large, and further a disconnection often occurs.
To solve such problems, a proposal has been made about a method of filling the opening with tungsten through a chemical vapor deposition method (CVD). However, according to this method, a manufacturing duration increases and further, the manufacturing cost is increased. This is because the method has a plurality of manufacturing steps.
Therefore, a suggestion has been made about a method of embedding an aluminum film in the opening by reflowing aluminum through a heating process, as disclosed in Unexamined Japanese Patent Publications No. H4-65831 and H1-76736. However, according to this method, a void is often caused to occur in the aluminum film where the opening is not sufficiently filled with the aluminum. In this case, the void means a space which is left in the aluminum film after the reflow. The void increases a contact resistance and often causes a disconnection to occur. Thus, where the void remains in the aluminum film embedded in the opening, such a void can not be directly detected from the outside of the substrate by an optical microscope because the void is left inside the aluminum film. Accordingly, the substrate must be cleaved or cut to detect the void inside the aluminum film by Scanning Electron Microscope (SEM).
However, this method can not be directly adopted for an actual product because the product must be destroyed. Therefore, an additional substrate for monitoring is prepared besides the product substrate. This additional substrate is cleaved to detect the void. However, this method requires an additional cost for manufacturing the additional substrate. Further, a forming state of the aluminum film embedded in the opening is different from each other between the product substrate and the monitoring or additional substrate. Consequently, the product substrate itself can not be correctly tested even when the monitoring substrate is checked.
Therefore, another proposal has been made about a method of checking the forming state of the aluminum film by arranging a test pattern region in addition to a product region on the same substrate. For example, the test pattern region has a test pattern which connects the openings in series. In this circumstance, the serial resistance is measured after the aluminum wiring pattern is formed to check the forming state of the aluminum film in the opening. Namely, the presence or absence of the void in the aluminum film embedded in the opening is checked by measuring the serial resistance. Although the forming state of the aluminum film in the opening can be tested without destroying the substrate in this method, the test should be performed after completion of the aluminum wiring pattern. In other words, the test can not be performed in the above method before completion of the aluminum wiring pattern. As a result, a long duration is taken to detect the void. Consequently, a plurality of defective products having the void are manufactured before the void is detected. This increases the manufacturing cost.
Another testing method has been suggested to detect the void before the aluminum wiring pattern is completed. In this method, the test pattern region is also provided besides the product region on the same substrate. In this event, the aluminum film in the opening is etched in the test pattern region to detect the void when the aluminum film in the product region is etched to form an aluminum wiring pattern. In this case, the void is detected by the SEM. However, the test pattern region must also be etched to detect the void in the above method. Namely, the test pattern region must be destroyed. In addition, the test can not be performed before the etching of the aluminum film is completed to form the aluminum wiring pattern in the above method. As a result, a relatively long duration is required to detect the void. Consequently, a plurality of defective products having the void are manufactured before the void is detected. This increases the manufacturing cost.